Electrometallurgy



Nov. 4, 1941. J. A ORME ELECTROMETALLURGY Filed Dec. 14, 1939 PatentedNov. 4, 1941 UNITED STATES PATENT OFFICE .rzrzzcrzzrsz... Applicationlslezlerlez No. 309,260

This invention relates to a method and means for the separation ofmetals by selective precipitation of metal ions from a gas phase ofvaporized metal and more particularly the invention provides a processinvolving vaporization of metals and selective precipitation in a purestate of the metals so vaporized under the influence of applied electricpotential. V

It is well knownthat the difllculty of obtain ing pure metals hashampered commercial as well as research activities employing metals.Chemical purification has been the best available means of freeing suchelements of impurities. But at best, the chemical agents used tend toadd impurities, although to a minor extent as com-- pared with theoriginal contaminating sub-' stances. Such conditions have naturallyresulted in a premium being placed on metals of a relatively high degreeof purity, as purity i separation of such elements from mixtures there--of in which the purification is carried out in the presence of onlythose contaminating substances which were present in the original masswhich is subjected to treatment, thereby avoiding contamination duringthe purification step, which process is capable of making extremelyaccurate separations of pure metals. It is an essential feature of thisinvention that metallic vapors be subjected to high potentialdiflerences of such naturethat the components of said vapors are causedto ionize and the metal ions are then precipitated on a suitable solidmeans by reason of potentials applied to the system. The process takesadvantage of the tendency of metals to migrate as ions from a cathode ina high vacuum to be deposited upon an object spaced a short distancetherefrom.

Other objects and advantages of the invention will be apparent from thefollowing detailed description thereof when considered in connectionwith the attached drawing, wherein:

Figure 1 is a diagrammatic showing of a preferred form of apparatus forthe purposes of the invention; and I Figure 2 is a cross-section of achamber for precipitation of metals.

Since a high degree of vacuum must be maintained in the apparatus forsuccessful operation, ore or other substance containing impure metal isfed from an air tight hopper l by means of and removed from the systemby vacuum pump 4." A supply of heat exchange medium is constantlycirculated through the Jacket 2 from inlet 6 to outlet 5. l

A hollow electrode the interior thereof [form's a'continu'ation of-thevertical shaft. Disposed below the open end of electrode I is a secondelectrode. 9 within the crucible l0. Material falling through the spacebetween electrodes land 8 is fused and vaporized too. large extent inthe are established between the said electrodes. High current densitiesare maintained between these electrodes at potentials ranging upwardfrom about 50 volts. In most l cated in broken lines.

operationsythe level of molten material isnot 'permittedto rise into thegap between electrodes but is maintained at about the level shown infull lines. However in the purification'of aluminum I and some othermetals of similar character, the level of fluid is preferably at thelevel 30 indi- In the latter case, the arc requires higher currentdensities. To provide adjustability electrode 9 is mounted on a screw l2or the like embedded in an insulator 29. Tap holes I are formed on theunder side of the crucible.

Metallic vapors produced in 'thefurnace 8 are passed therefrom throughconduit I 3. to the selective precipitation-chambers '23. In each ofthese chambers there is a pair of electrode grids l5 and IS, a plate l8and a control electrode 20.

Each of these electrodes and the plate in the precipitation chamber issuitably insulated from the walls'thereof, the plate It being mounted ininsulating blocks ll while the control electrode 20 is provided with aheavy insulator 2| because of the high potentials normally appliedtothis member during operation of the chamber.

parallel, or in series as shown. In the embodi ment illustrated, thelower end of a second cham- I is provided in'the upper end of furnace;8, preferably so positioned that Surrounding the plate I8 is aninduction coil which serves a purpose to be hereinafter morefully debe!23 is connected to the first chamber by a conduit 22, while a conduit 24furnishes a communication between chamber 23 and a trap 25 for theremoval of substances which are injurious to the vacuum pumps 26 and 21from the gases to be 'removed from the system. These pumps are requiredfor the elimination of occluded gases and the like.

Each chamber 23 acts to precipitate metal selectively upon the plate llas indicated generally at 20. Conditions within the chamber are soadjusted that grid I6 is negative with respect to grid I and controlelectrode 20, establishing a virtual cathode in space. Metallic vaporsare ionized between the furnace electrodes and grid l5, migrate to gridIt and, under the influence of a high positive potential on controlelectrode 20 are projected toward said control electrode and depositedon the plate l0. to which no potential is applied. The mechanism of theprocess is not thoroughlyunderstood but it is lmown that metals may beseparated thereby in a state of phenomenal purity with the expenditureof a very small amount of power.

The potentials applied to various parts of the apparatus are capable ofwide variation, but a number of experimental runs on various types ofmetallic mixtures indicates that very good results are obtained byestablishing a potential difference in excess of 50 volts between thefurnace electrodes 1 and 8 while the grid is is maintained at a positivepotential of 100 to 1000 volts with respect to the closer furnaceelectrode (electrode 1 in the embodiment illustrated). It appears to beimportant that the current between the furnace electrodes be relativelyhigh, usually at least 100 amperes, preferably between 100 and 500amperes. All conductors for applying potential to the apparatus arepreferably connected to sources of potential adapted to rather flexiblecontrol in order that relative potentials may be varied within widelimits. One suitable means for accomplishing this result is the powerpack indicated generally at 32. This enables the operator to cleandeposits of metal from those parts of the apparatus not intended toreceive the same by bombardment.

Grid I 6 is conveniently maintained at a proper potential with respectto grid l5 by connecting the former to electrode I, but it is'advisablein most cases to provide an independent control on the source ofpotential for each of the electrodes.

It has been found that the selectivity of metal deposit on plate I! maybe readily controlled by maintenance of proper values for two importantvariables. namely pressure and the potential of control electrode 20,which latter should be at least 1000 volts greater than that of grid ll.Palladium is deposited at the highest pressure and the lowest positivepotential on electrode 20 of any of the metals investigated. Thefollowing series shows the order in which a number of metals aredeposited under conditions of decreased pressure and increased controlpotential at electrode 20: Palladium, gold, silver, lead, tin, platinum,copper cadmium, nickel, indium, and iron.

In addition to the above. aluminum has been selectively deposited. Thismetal cannot be accurately fitted into the series at present.- It wasfound that this particular element is best. deposited in a rareatmosphere of a mono-atomic gas such as helium.

The following specific examples illustrate preferred operations inconnection with two of the precious metals.

Example I.-silver was deposited at an absolute pressure of l x 10- mm.of mercury using substantially the following potentials with respect tofurnace electrode 1:

Volts Furnace electrode 0 --150 Grid ll +200 Grid ll +100 Controlelectrode II +12,000

Example II.Gold was deposited at an absolute pressure of 2 x 10-' mm. ofmercury and substantially the following potentials with re- Forsuccessful operation the pressure should be maintained at a value notsubstantially in ex-' cess of 1 mm. of mercury, absolute, but commercialoperation normally requires lower pressures for successful operation.

' When a substantial deposit of metal has been built up on the plate ll,an alternating current may be passed through the induction coil II,thereby setting up eddy currents in said metal to melt the same. Themolten metal may then be tapped oil! through the port II.

It will be readily understood that the process is capable of widevariation within the scope of the invention, but it appears that bestresults are obtained when plate I! is positioned in the region of thechamber corresponding to the "Crookes dark space" of the chamber, whichchamber is. in effect, a vacuum tube of the vowels "type.

I claim:

1. A process for separating a pure metal from a sub tance containing thesame comprising subiecting said substance to conditions to vaporizemetallic constituents thereof, passing the resulting vapor at a pressurenot substantially greater than 1 mm. of mercury to ne end of an enclosedprecipitation -zone, maintaining adjacent said end in succession a firstregion of electric potential, a second region of potential negative withrespect to said first region, a third region of potential at least 1000volts positive with respect to said second region and depositing saidmetal on a solid object between said second and third regions.

2. aprocessaccordingtcclaimlcharacterised in that said constituents arevaporized in an electric are under a potential of at least bllvoltl andcurrent of at least amperes.

3. Aprocess accordingtoclaimlforpreparing pure gold characterized inthat said constituents are vaporized in an electric are under apotential of at least 50 volts and a current of at least 100 amperes,passed to said zone from one end of said arc and that the potentials ofsaid region! with respect to said end of said are are substantially asfollows:

4. A process according to claim 1 mming pure silver characterised inthat said constituents are-vaporized in an electric arc imder apotential of at least 50 volts and a current of at least 100 amperes,passed to said zone from one end of said are and that the potentials ofsaid regions with respect to said end of said arc are substantially asfollows:

Said first region+200 volts Said second region+100 volts Said thirdregion+12,000 volts 5. In an apparatus for separating metals includingmeans to vaporize metallic material and means to selectively precipitatemetals from ma-

